1. Field of the Invention
The present invention relates generally to a method and arrangement of restoring normal operation of a data terminal equipment(s) in a multipoint data communications system, and more specifically to such a method and arrangement wherein a training signal is requested in the event of divergence of an automatic equalizer of the data terminal equipment.
2. Description of the Prior Art
It is known in the art that in a multipoint data communications system, a single primary station is connected to two or more secondary stations. The primary station is able to send data that is addressed to one or more of the secondary stations. However, a secondary station is permitted to send data only to the primary station; and one secondary station is unable to send data to another of the secondary stations. Each of the primary and secondary stations includes, a data terminal equipment (DTE) such as a computer and a modem which is coupled thereto. The primary and secondary stations are interconnected via a public switched telephone network or dedicated telephone lines.
In the event that an automatic equalizer of one secondary station diverges due to degradation of transmission path and hence is no longer able to normally operate, it is vital to normalize, as early as possible, the operation of the automatic equalizer rendered inoperative.
According to a known method of restoring the operation of an automatic equalizer which has been rendered inoperative due to divergence thereof, the modem including the equalizer in question acquires data which are exchanged between the primary station and one of the other normal secondary stations. In more specific terms, the secondary station, which includes an automatic equalizer in divergence condition, adjusts its own automatic equalizer using the acquired communications signals, and establishes regular communications with the primary station.
The above-mentioned known technique has been found suitable for the communication speed up to as high as 9,600 bps (bits per second) for example. However, in the case of the communication speed of more than 19,200 bps, the prior art has encountered the difficulty that a large amount of time is undesirably required to pull in or converge an automatic equalizer.